1. Field of the Invention
The present invention relates to a power transfer device for four-wheel drive vehicles, and more particularly to a lubrication mechanism for an ancillary change-speed mechanism in the power transfer device.
2. Description of the Prior Art
In U.S. Pat. No. 4,713,980 granted to Ida et al. on Dec. 22, 1987, there has been proposed a power transfer device adapted for use in combination with a power transmission, which comprises a housing adapted to be secured to one end of a casing of the power transmission, an input shaft rotatably mounted within the housing for drive connection to an output shaft of the power transmission, an output shaft rotatably mounted within the housing and arranged coaxially with the input shaft for relative rotation thereto, an ancillary change-speed mechanism in the form of a planetary gear unit arranged within the housing and having an input element mounted on the input shaft for rotation therewith and an output element connectable to the output shaft, and a clutch sleeve axially slidably mounted on the output shaft and shiftable between a first position in which it is retained to effect a drive connection between the input and output shafts and a second position in which it is retained to effect a drive connection between the output element of the planetary gear unit and the output shaft.
In the power transfer device described above, an oil pump assembly is mounted on the input shaft at the outside of the housing to be driven by rotation of the input shaft and is arranged to pump up lubricating oil stored in the housing and supply it into an axial bore in in the input shaft for lubrication of the components of the planetary gear unit. In such an arrangement of the oil pump assembly, however, the input shaft has to be extended for mounting thereon the oil pump assembly, and also the housing has to be enlarged for containing therein the oil pump assembly. This results in an increase in size and weight of the power transfer device.